This invention relates to an air dryer assembly for a compressed air system, such as, for example, a compressed air braking system for commercial vehicles, and more specifically to a membrane air dryer and method and apparatus for mounting a membrane dryer.
Commercial vehicles such as trucks, buses, and large commercial vehicles are typically equipped with a compressed air braking system in which the brakes of the vehicle are actuated by compressed air. An air compressor is operated by the vehicle engine and storage reservoirs maintain a quantity of pressurized air for the brakes and other compressed air uses. Moisture and oil are two attendant problems associated with compressed air systems and are particularly problems that can adversely affect brake system operation.
As a result, an air dryer is incorporated into the compressed air system to effectively remove moisture from the system. Typically, an air dryer contains a desiccant material that adsorbs moisture from the compressed air from the compressor. However, desiccant dryers become saturated, and as a result, require a purge cycle. During the purge cycle, the compressor does not supply compressed air to the system and a backflow of air purges the desiccant material of its moisture content.
Membrane air dryers have been used to provide a continuous flow of compressed air to the system. Membrane air dryers allow for a continuous flow of compressed air through a packet of small, hollow tubes within a tubular membrane dryer housing. The hollow fibers are typically a porous plastic material that are coated with a special material that causes the tubes to be permeable to water vapor, but not air. Thus, as air is passed through the membrane dryer hollow fibers, water vapor permeates the fiber walls and collects on the outside of the hollow fibers. Meanwhile, dry air is permitted to pass through to the rest of the system. In order to avoid the accumulation of water vapor on the outside of the fibers, thereby saturating the system, a portion of the dried air is permitted to pass back through the membrane air dryer, this time on the outside of the fibers. The backflow of air is allowed to expand, pickup the water vapor on the outside of the tubes, and then exit the membrane air dryer, typically to atmosphere. Furthermore, since oil vapors, liquid water, carbonous materials, and other contaminants reduce the effectiveness of the membrane air dryer, a filter is typically provided upstream of the membrane air dryer.
While membrane air dryers have been established as competitive technology to desiccant dryers in plants and laboratories, membrane air dryers have not been notably implemented on vehicles for compressed air systems partially due to the difficulty in mounting the membrane air dryers to the vehicle. In the past, membrane air dryers have been incorporated into the main air reservoir of the air brake system. However, such mounting configurations do not provide easy access to the membrane air dryer for regular maintenance, inspection, repair or replacement.
Furthermore, typical mounting structures for membrane air dryers require a separate set of mounting brackets for securing the membrane air dryer to a vehicle.
Accordingly, a need exists for a membrane air dryer design that can be effectively and efficiently mounted to a vehicle in a location that provides relatively easy access for maintenance, inspection, repair or replacement.